Control mechanism for furnaces



Aug. 16, 1938. R. MIHARDGROVE CONTROL MECHANISM FOR FURNACES Filed March 12, 1955 2 Sheets-Sheet l INVENTOR Ralph M. Hardgrove.

BY mz ATT NEY- FLOW RESPONS/VE Aug. 16, 1938. R. M. HARDGROVE CONTROL MECHANISM FOR FURNACES Filed March 12, 1935 2 Sheets-Sheet 2 RESPONSIVE (W ATT m m m Rm mH N J Em VH/ p M P 7 z a L m w my M 4 2 Patented Aug. 1 6, 1938 r CONTROL MECHANISM Fort FURNACES Ralph M. Hardgrove, Westfield, N. J., assignor to Bailey Meter Company, a corporation of Delaware Application March 12, 1935, Serial No. 10.667

4 Claims. (01. ma -2s) In connection with the operation of furnaces and especially furnaces utilizing fuels burned in suspension, such as oil, gas, or pulverized fuel, the danger exists that in kindling a. fire an exploslon may occur if, at the timeof lighting, an explosive mixture of fuel and air is in the furnace. To avoid this it is the practice in kindling a fire in a furnace to first thoroughly purge orscavenge the furnace by effecting a flow of air through it. This may be done by natural draft or by starting up one of the draft fans, usually the induced draft fan, and operating it for a length of time sufhciently to thoroughly purge or scavenge the furnace, after which the fan may or may not be stopped as found desirable and the fire lighted.

In my prior Patent No. 1,914,949, granted June 20, 1933, I have disclosed and claimed a method and apparatus of control mechanism for a furnace whereby it is not possible for an operator to supply fuel to a furnace and kindle a fire therein without having first scavenged the furnace and whereby if having scavenged'the furnace .he delays kindling the fire until the air flow through the furnace decreases below a certain value, then he mustagain scavenge the furnace in order that he may supply fuel thereto. By this arrangement there is avoided the possibility that the operator may scavenge the furnace, delay kindling the fire until the scavenging may have become ineffective, and then kindle the fire without properly again scavenging the furnace. l 7

My prior patent is further directed to provide in connection with afurnace afuel supplying means, a fuel igniting means, and a control means whereby the fuel supplying means and the fuel igniting means cannot be rendered operative until a predetermined flow of air obtains in the furnace, the arrangement preferably being such that, the fuel supplying means cannot be operated until after the fuel igniting means has been started. H l

Modern furnaces, and particularly boiler' furnaces, maybe equipped with a large number of separate burners for pulverized fuel, oil or gas, and in some cases, there maybe as high as twenty or thirty such burners for an individual furnace. The kindling or lighting off of such a furnace presents a problem to the solution of which the method and means of the present invention are directed.

One object of my inventionis to provide an improved construction and arrangement of con-- trol mechanism for a furnace whereby the fuel igniting means cannot be made operative until a predetermined flow of scavenging air ;e xists through the furnace and whereby thefuel feed-ly ing means preferably cannot be operated until the fuel igniting means have been started,

Another object of the invention is to provide in connection with a furnace having .a plurality of fuel burners an interlocking arrangement such that the ignitingmeans will be effective for each and. every burner at which the fuel supply is available to obviate the possibility that the igniting means might function in front of a burner at which fuel is not available, while another burner some distance away was feeding fuel to the furnace but the igniting means for that burner was not effective, thus resulting in a loading of the furnace with a mixture which eventually might become ignited with disastrous effects.

, A further object is to provide an interlocking arrangement such that if and when fuel is available through a burner its fuel igniting means is made operative.

A-still further object is that the main fuel supply to all of the burners of a boiler closes upon the failure of air flow through the furnace below a predetermined value, or upon failure of flame within the furnace.

Still another object is an interlock arrangementresponsive not only to the rate of air fiow through the furnace but also to the rate of supply of fuel to the furnace.

Still further objects will become apparent from a study of the drawings and specifications relating thereto.

For a consideration of what I believe to be novel and my invention, attention is directed to thereto.

In the drawings:

Fig. 1 is a diagrammatic view of a furnace Referring first to Fig. l, 1 indicate therein a.

furnace l which may be of any suitable type, but shown in the present instance as being a furnace for heating a boiler having boiler tubes indicated at t.

At 3 is indicated a fuel supply for the furnace and in the present instance represents a gas supply line from which a maincontrol valve t for the boiler 'l controls the supply of gaseous fl lel to a header'ficommon to all'of the burners supplying the boiler l. The fuel supply, or gas line 3, is to be taken asltypical .of any suitable means for supplyingfuel to a furnace and may represent, for example, a means for supplying oil, gas, pulverized fuel or the like. In the present instance the control valve 4 is spring loaded by a spring '3 to normally closed or shut off position and adapted to be opened for flow there- 'through by the energization of a solenoid I.

In Fig. 1 I illustrate a single burner and its control leading from the header 5 to the furnace I, while in Fig. 2 I showa plurality of such burners and the interlocking control circuit therefor. The single burner and related apparatus of Fig. 1 may be considered as the only burner feeding the boiler I, or may be considered as one of the plurality'of burners illustrated in Fig. 2. Likewise the three burners constituting the plurality of burners of Fig. 2 may all be feeding the furnace I or may be a part only of a larger number of burners all related to the furnace I.

Referring particularly to Fig. l, a pipe 3 leads from the header 5 to a burner 9. Interposed in the pipe-3 are two control valves I 2, II whose functioning and purpose will be described hereinafter.

Theburner 3 extends through a wind-box l2 supplied with forced draft by a motor driven blower I3. or gas torch, for use in kindling or lighting the furnace. The flow of fuel through it is controlled by a valve I5 adapted to be opened by a solenoid I3 and closed by a spring I I6. At I1 is an igniting means for the torch, such as a spark plug. It is connected to the secondary winding of a transformer I3.

I3 indicates the stack of the furnace and 20 indicates an induced draft fan driven by an electric motor 2I. The furnace construction so far described is illustrated only diagrammatically and by way of example and is to be taken as representative of any suitable. furnace provided with a fuel feeding means and a means for effecting flow of air through the furnace.

According to the embodiment of my invention illustrated in the drawings I provide a mechanism 22 which is responsive to the rate of flow of air through the furnace and I provide such device with a contact closing arm 23 which when the flow of air through the furnace reaches or exceeds a predetermined value effects the closing of a pair of contacts 24. Contacts 24 are biased toward open position so that they are. open except when held closed by the flow responsive mechanism.

In the present instance the flow responsive device is shown as comprising a casing 25 in which is a sealing liquid, such as oil, for sealing two inverted bells 26, 21 connected to opposite ends of a lever arm 23 pivoted centrally to a flxed point. Contact arm 23, is connected to lever arm 23 and forms a part of it. The arm 23 extends at an angle to the lever arm 23 and is weighted by means of a suitable weight 29, which biases the bell structure to a position as shown in the drawings, which position it occupies at no air flow through the boiler furnace. When arm 23 is moved into engagement with contacts 24 it moves toward vertical position but does not move beyond the vertical, that is beyond dead center. Ittends always therefore to move toward the position pressure which bears a definite relation to the rate of flow of air and/or products of combustion through the furnace. In the present instance the I4 indicates a torch, such as an oil way of example and that the connections may bemade to any two suitable points, the essential thing being that the bells be subjected to a difl'erential pressure of sufficient value to eifect the operation of the flow responsive device 22.

The movable element of contact 24 is connected by conductors I30, Hi to one side of electrical supply lines 32. Interposed between the conductors l3lI, I3l is a flame failure detector 33 which may comprise electrodes of a carbonaceous material such, for example, as silicon carbide positioned in the path of the flame within the furnace. While I have shown but asingle flame failure detector positioned adjacent one of the burners of Fig. l and Fig. 2, it is my concept that there might be a single flame failure detector for an entire furnace, or one for each burner of a furnace (Fig. 3), or intermediate number.

Shunted across the flame failure detector 33 is a switch blade 34 shown in open position. The stationary element of contacts 24 is connected by a conductor 35 to the other side of the supply lines 32, such conductor including the winding of a solenoid 36. Solenoid 38 has a pair of contacts 31 which are bridged, or close-circuited, whenever solenoid 36 is energized.

The primary winding of transformer I8 and the winding of solenoid it are connected in series to one of the supply lines 32 by conductor 38, including the contacts 31 of the solenoid 36. The other side of the transformer primary winding is connected to the other supply line 32 by a conductor 39, hand switch blade 42, and conductor I3I; conductor 38 including contacts 40 which are open-circuited at all times the valve II is closed.

When valve II is opened through the agency of hand wheel SI, then contact bar 4I immediately engages and closes the circuit of contacts 40. throughout all positions of opening of the valve I I.

The switch blades 34 and 42 are Joined for simultaneous operation and with them a third switch blade 43 which Joins conductor 38 with a conductor 44, the latter leading to the winding of solenoid I. A conductor 41 joins the other terminal of solenoid I with a hand operable switch 48 connected by conductor 43 to the electrical supply lines 32. Solenoid I when energized is adapted to close the circuit across the contacts 45, thus by-passing the switch blade 43 to lock valve 4 in an open position.

.4 may be traced as follows; power line 32, conductor 46, switch 43, winding of solenoid 1, con- .ductor 44, switch blade 43, conductor 38, and contacts 31 to the other side of power line 32. As previously mentioned the switch blade 43 may be by-passed by a holding-in circuit including the contacts 43.

In the pipe 3 in the direction of gas flow to the burner 3 is located a hand operable valve III of a bleeder typehaving a small bleeder port 50 leading to the atmosphere and arranged so that when the valve I0 is closed off the bleeder port 50 is opened to the atmosphere to bleed from between the valves IO and II any gas leakage past the valve ll toward the furnace. The valve II located in the pipe 3 between the valve III and the burner 3 is of a hand operable type adapted in its closed position to open-circuit the contacts 40 and thus effectively de-energize solenoid I8 and transformer primary ll. When solenoid It is so deenergizedthe spring H6 immediately closes the representative of a plurality of burners similar to the burner 9 of Fig. 1, and each provided with a torch and igniting means as in Fig. 1. The

' various equipmentand arrangement of Fig. 2 is similar to that of Fig. 1 except that in Fig. 2 I illustrate diagrammatically my proposed arrangement of interlocking for operation of the various burners of a plurality of burners on a single furnace. The valves l8. IOA, I03 may be similar. to the valve in of Fig. 1 and may be provided with leakage'ports 50.

The circuit for controlling and igniting each torch includes the primary of the transformer l8, the solenoid l 6, and the contacts 48, in series with each other across the conductors 38, 49. For a plurality of burners, as in Fig. 2, the igniting circuit for each of the burners-is connected in parallel across conductors 38, 49. The arrangement .is such that the torch valve I5 is closed (by spring H6) and transformer I8 ineifective when the fuel supply valve H is in a tight closed position whereby contact bar 4| does not short the contacts 48. Immediately the valve ll begins to open and for all positions of opening, the contact bar 4i shorts the contacts 48, energizing solenoid IE to open the torch supply valve l5 and at the same time energizing the transformer l8 to actuate the igniting spark l1. This, assuming for the moment that conductors 38, 49 are alive.

Conversely when the valve II is closed, thus stopping the flow of fuel through the burner 8. immediately the torch l4 and igniter II are made ineffective, regardless of the condition of the remainder of the electrical circuit. This prevents the possibility of an igniting flame opposite a burner through which no fuel is being admitted to the furnace. As will be seen hereinafter, the arrangement is such for each of the burners as to prevent the possibility of having fuel admission through a given burner without having the igniting means and torch operative for igniting same. r

The arrangement just briefly described primarily effects a safeguard against fuel being admitted through the .burner 8, for example, to the furnace with the igniter l1 and torch l4 inoperative and at the same time no-fuel being admitted through the burner 93 while the igniter B and torch MB were operative. This hazardous condition which is prevented by my arrangement would allow on a large modern furnace for the feeding of a considerable volume of fuel through one burner to the furnace at a distance of possibly 15 to 20 feet from the point where the torch was lighted, and thus the filling to a large extent of the furnacewith a combustible'mixture before the same became ignited.

The operation is as follows:-

Assume that the furnace is shut down and that it is desired to kindle same. The air-flow responsive device it will occupy the position illustrated in Fig. 1, namely, contacts 24 being open.

operator first effects a flow of air through the furnace to scavenge it. This may be done by natural draft or by means of the induced draft fan, the forced draft blower, or both, the means by which the flow of air is established, depending upon the nature of the particular furnace installation to which the invention is applied. The essential thing is that a flow of air be established through the furnace to scavenge it and that until the contacts 4%.

The

such a flow "of air of a definite predetermined magnitude is established the furnace cannot be kindled. e i

As the flow of air through the furnace increases a differential pressure is appliedto the flow responsive device 22. which differential increases a with the rate of flow in known manner. As soon as a predetermined rate of flow is reached the differential pressure applied to bells 28, 21 will be sufficient to turn lever arm 28 on its pivot in r a clockwise direction and move contact arm 23 to a position wherein it closes the contacts 24. The arrangement is such that a predetermined flow of air and/or gases through the furnace is required before the contacts 24 are close-circuited.

The closing of contacts 24 completes one step in the sequence necessary to ene gize the solenoid 38. When the switch blade 34 is closed (by-passing the flame failure detector 33) solenoid 36 is energized closing contacts 31 for the energization of conductor 38.

Simultaneously with switch 34 the switch fingers 42, 43-are closed; switch 42 energizing conductor 48, and switch "accomplishing one step in completing the circuit to the fuel supply valve solenoid I, which is further controlled by switch The switch 34, 42, 43 may be closed by the operator either before or after purging the boiler.

Assume for the moment that the boiler has been purged, contacts 24 closed and that switch 34, 42, 43 islikewise closed. The resulting energize.- tion of solenoid 36 will cause contacts3i to close, making energy available on conductors 38, 49 and also effecting energization of the circuit of solenoid 1 except for the switch 48.

Switch 48 may be closed now or later. If closed at this point, fuel will be available at valves Ill. IOA, IOB, or if these valves are open then at valves II, A, B. If for example, valve II is open then its opening will have completed the circuit between conductors 38, 48 for energizationof torch valve 5 and ignition transformer l8 so that torch I4 is available for lighting burner 8 when fuel arrives.

Valve ll may be opened either before or after main supply valve 4. If opened prior to the opening of valve 4 then immediately as it unseats, the torch i4 is lighted and is thereafter available when solenoid I is energized and gas flows through the burner 8. i

As long as switch 34, d2, 43 is closed each igniter becomes active as soon as its valve II is opened and stays active until switch 34', 42,43 is opened, which can only be done after detector 33 is heated up and passes current through the flame.

' With the closing of contacts 31, d3, t8 the solenoid l is energized and immediately completes a holding circuit around contact d3 by a hand switch it may be pulled. it air flow decreases to a predetermined minimum then contacts 2 will automatically open tie-energizing solenoid 36, opening contacts ill, and thus deenergizing solenoid l to shut off the fuel supply.

Similarly should flame fail at the detector 33 it de-energizes solenoid 36 resulting in a closure of main fuel valve 4.

It will be observed that the main fuel supply to the furnace, as well as the ignition and kindling means for each and every burner, are all under the direct control of the air flow responsive contact 24 and/or the flame detector 33. It will be understood that the circuit may be arranged to have a detector 33 opposite each of the burners or one detector common to all of the burners. Fig. 3, for example, illustrates an embodiment wherein there is a detector 33 opposite each burner.

In brief, after the furnace is in operation the solenoid 36 controls the supply of fuel to the thermore the switches 34, 42, 43 have been omit ted and each igniter is ready at all times to act. All that is required is that the detector 33 be cool and that contacts '40 be closed.

The circuit for the solenoid i is under control of the hand switch 43 and the flow responsive switch 24. The ignition and torch means of each burner are under the control of flow responsive switch 24, detector 33,and contacts 453.

In kindling the furnace switch 24 automatically closes when the air flow reaches a predetermined value. The detector 33 being cool, the solenoid 62 is in the shown position with contact 63 closed and as soon as valve ll begins to be opened (closing contacts 40) flow-is established through torch l4 and igniter i1 is actuated. This regardless of whether or not hand switch 43 has previously been closed, thus opening valve 4.

Any or all of the burners 3, 3A, etc. may be lighted off in this manner, for the ignition and torch means are always available, and as soon as any valve II is opened thus closing contacts 40, the torch will be lighted, if a predetermined flow of air exists whereby contacts 24 are closed.

During operation if-at any time air flow falls to a predetermined minimum, the switch 24 will open, thus closing the fuel supply valve 4 for the furnace. Failure of flame at a detector 33 deenergizes solenoid 62, closing contacts 63 whereby the ignition means immediately comes into play and assuming that valve ll remains open, it lights it off immediately. If, however, valve H has been closed then the ignition means remains in condition to immediately function upon opening of valve ii.

The common flame detector of Fig. 2 could still be retained to close valve 4 if desired.

In Fig. 4 I show a further embodiment of my invention applied to a plurality of burners, each equipped with torch and igniting means, but for the sake of simplicity I have not included in this part of the drawings the flame detectors 33, although it will be understood'that they may be applied to this arrangement as well as to the ones previously described. Herein I introduce a further safety feature, namely, in connection with the rate of supply of fuel to the plurality of burners.

The torches l4, I4A, I43 are supplied with gaseous fuel from the conduit. 3 ahead of the valve 4 I indicate at 13 an orifice, or other restriction in the pipe line 3, for creating a pressure diflerential bearing a known relation to the rate of flow of fuel through the pipe 3 toward the burners 9. Connected to be responsive to such differential pressure is a diaphragm meter 12 adapted to close a switch 14 when a predetermined rate of fuel flow exists.

The hand switch 15 is used to start the furnace and indicates the contacts of the air flow responsive device 22 previously mentioned. 64 and 65 indicate solenoids, the former controlling contacts 66, 6'! and the latter controlling contacts 68, 69. The various torch controlling solenoids l6 and ignition transformers iii are for each burner connected in parallel across conductors W, H.

[it i I have indicated a coil, such as the solenoid I of the remainder of the drawings and which may be a torque motor or a thruster.

The requirement being that the valve 4 remain open only when the coil 1 is energized.

In kindling the furnace of Fig. 4-1 assume first that switches 14,15, and 24 are open as indicated. The furnace is purged or scavenged by effecting a flow of air and/or gases sufllcient to actuate the device 22 and close the contacts 24. Such closure energizes solenoid 64 which closes contacts 66, 61. If it is now desired to kindle the furnace, starting switch 15 is closed by hand,- which in conjunction with contacts GB- eil'ects energization of solenoid 65, thereby closing contacts 68, 69. Fuel supply valve 1 opens due to energization from a circuit completed through contacts 61 and 68 but no gaseous fuel flows toward the burners unless the various hand valves at the outlet of valve 4 and the valves iii in individual burner lines are opened.

Simultaneously with the energization of the coil 1, occurs actuation of each and every torch valve l6 and igniting transformer l8 through a circuit controlled by contact 69. v The torches are all lighted irrespective of whether gas is being supplied through each or all of the burner pipes 9, 9A, 3B. Whichever one of the burner pipes has gas flowing through it will then be kindled. As soon as a predetermined flow of gas occurs through the valve 4, effective upon the meter 12, the switch" is closed, thus by-passing contact 68 and locking in the coil '5 whereby valve 4 stays open even after the ignition means are extinguished by opening the starting switch 15.

After the furnace is in operation if at any time the gas flow through the orifice 13 decreases to a predetermined minimum then the switch 14 is opened, de-energizing coil 1 and closing valve 4. Before valve 4 can again be opened and gas admitted to the furnace the starting switch 276 must be closed by hand to actuate solenoid 65.

During operation the entire fuel supply and igniting system is under the control of the air flow actuated switch 24, so that if air flow through the furnace decreases to a predetermined minimum, switch 24 opens deenergizing solenoid 36, opening contact 61, and closing fuel supply valve 4.

In connection with all four of the figures of the drawings it will be seen that by my invention in starting the furnace the operator must first effect a flow of air through the furnace so as to thoroughly scavenge or purge it prior to kindling creases by a certain amount. By this means the draft through the furnace may be decreased somewhat over that required to close the contacts 24, and still the contacts will remain closed, which means that if desired the arrangement may be such that a stronger draft must be used to scavenge the furnace, after which the draft.

may be shut down somewhat during the kindling operation.

It will be. understood that it is not absolutely necessary for the air supply responsive mech-- anism to be interlocked with both the fuel supplying means and the fuel igniting means as I may utilize an arrangement wherein the air supply responsive means is interlocked only with the fuel supply means or only with the fuel igniting means.

It is to be understood that while I have illustrated my invention in connection with a furnace burning gas, this is only by way of example, and that the invention may be utilized in connection with furnaces burning other fuels, such as oil or pulverized coal for example. Furthermore it is not necessary to have the furnace arranged for heating a vapor generating boiler, but'the furnace may be of any type or for any service.

Various forms of apparatus may be incorporated in the system. For example it is not essential that all of the interlocking be done electrically. It may be readily accomplished hydraulically or by pneumatic means and instrumentalities differing from those which I have illustrated and described may readily be adapted to the invention.

In accordance with the provisions of the patent statutes I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiments thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

.What I claim as new, and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination with a furnace having a plurality of burners, a conduit for supplying fuel to all of said burners, a main valve in said conduit, means responsive to the flow of air through said furnace, means controlled by said first named means for opening said main valve when a predetermined or greater rate of air flow exists through said furnace and closing said valve when the rate ofv air flow falls below said predetermined rate, an individual burner valve for admitting fuel to each of said burners, fuel igniting means associated with each of said burners, and means under the joint control of said first named means and each flame responsive device to insure that the corresponding ignitthrough said furnace and closing said valve when the rate of air flow falls below said predetermined rate, an individual burner valve for admitting fuel to each of said burners,fuel igniting means associated with each of said burners, means permitting operation of each of said igniting means when the corresponding burner valve is open and preventing operation of the igniting means when the corresponding burner valve is closed, means under the joint control of said first named means and each flame responsive device to insurethat the corresponding igniting means will be operated in the absence of flame from the corresponding burner and rendered inoperative in the presence of flame from said burner.

3. In combination with a furnace having a plurality of burners, a conduit for supplying fuel to all of said burners, a main valve in said conduit, means responsive to the flow of air through said furnace, means controlled by said first named means for opening said main valve when a predetermined or greater rate of air flow exists through said furnace'and closing said valve when the rate of air flow falls below said predetermined rate, an individual burner valve for admitting fuel to each of said burners, fuel igniting means asociated with each of said burners, and means under the joint control of said first named means andeach flame responsive device to render said igniting means operative in the absence of flame from the corresponding burner and when said predetermined or greater air flow exists through the furnace; and to render said igniting means inop'erative in the presence of fiame from the corresponding burner or when the air flow through the furnace falls below said predetermined rate.

4. In combination with a furnace having a plurality of burners, a conduit for supplying fuel to all of said burners, a main valve in said conduit, means responsive to the flow of .air through said furnace, means controlled by said first named means for opening said main valve when a predetermined or greater rate of air flow exists through said furnace and closing said valve when the rate of air flow falls below said predetermined rate, an individual burner valve for admitting fuel to each of said burners, fuel igniting means associated with each of said burners, and means under the joint control of said first named means 

